Crossrail, the largest construction project in Europe, is facing two investigations by the health and safety regulator over allegations made by a whistleblower about the circumstances that led to the death of a worker earlier this year.

The Observer has learned that the Health and Safety Executive (HSE) is acting on a series of statements from the whistleblower in which safety standards on the £15bn project have been condemned.

Among the former Crossrail worker's claims is that the death of Rene Tkacik, 43, who was struck by a falling slab of concrete in Holborn on 7 March, could have been avoided. At the time of his death he was spraying concrete through a hose – a process known as "shotcreting" used by Crossrail contractors since last year.

The whistleblower has told the HSE that a number of workers had already been injured by falling shotcrete in the part of the tunnel in which Tkacik was working.

A statement given by the whistleblower to the HSE in June, seen by the Observer, claims that concrete regularly fell on and around workers, although usually in small handfuls.

The statement says: "During my time working on the project I saw shotcrete fall on many occasions. Normally this was within the first few hours of it being sprayed. I saw a few near-misses. The area where the spraying was taking place was often surrounded with red and white tape, but people walked in this area if they needed to be there."

A spokeswoman for BBMV, the joint venture of four private contractors operating in the part of the tunnel where the whistleblower was working, said some of the specific accusations made by the whistleblower were untrue.

She said: "There are specifics within this account that have no foundation in truth. As an example, our construction methodology for the application of shotcrete with mandatory exclusion zones does not allow for the incidents detailed to occur.

"The HSE has visited our Finsbury Circus and Whitechapel sites as part of their Crossrail inspection programme and is fully satisfied with our arrangements.

"BBMV take all safety concerns or suggestions for improvement seriously. The concerns raised have already been addressed, are being addressed or were investigated as appropriate at the time."

The HSE has started one investigation into the death of Tkacik and another into claims by the whistleblower about his own experience and injury, working with shotcrete in the tunnel. Tcakik was killed on a part of the project being worked on by Bam Ferrovial Kier Joint Venture.

An HSE spokesman said that it could not comment on any ongoing investigations.

Helen Clifford, a solicitor acting for men injured on Crossrail, said that a BBC documentary on the engineering at Crossrail failed to reflect the real state of the project.

She said: "The death of Rene Tkacik occurred as a result of falling shotcrete.

"The whistleblower confirms that the men were told to work under freshly applied shotcrete to remove the excess and this is something that he did on many occasions.

"Crossrail/BBMV were aware of shotcrete falls, but continued to require men to work in those conditions. Had they implemented a safe system of work, Rene's death might have been prevented.

"The BBC documentary focuses on the engineering challenges and key milestones of delivering Europe's biggest construction project. However, the human cost of the project has been buried as deep as the tunnels in which the men are working."

Earlier this year documents leaked to the Observer revealed that industrial relations were close to collapse and workers too scared to report injuries for fear of being sacked. Crossrail managers were accused of photographing or videoing contractors' staff who may be in danger and emailing it to others "with unmasked glee".

The onsite culture of the east-west rail link was said to be "almost entirely counterproductive" to delivering the project safely, on time and on budget. It adds that injured workers were "afraid to report due to the likelihood of being laid off".

BBMV said then that the report was not a true and accurate reflection of its safety culture.

• This article was amended on Sunday 3 August 2014 to clarify that Tcakik was killed on a part of the project being worked on by Bam Ferrovial Kier Joint Venture.